1. Field of the Invention
The present invention relates to a medical image processing apparatus and a method of processing a medical image for processing image data collected by a medical modality of an X-ray CT scanner or the like, particularly relates to a medical image processing apparatus and a method of processing a medical image accompanied by a step of removing a region of the blood vessel from an image.
2. Description of the Related Art
In a field of medical diagnosis based on an image collected by a medical modality, an X-ray CT scanner constitutes one of central presences thereof.
By using an image provided by the X-ray CT scanner as a simple CT image as it is, morphologic information in a subject can be provided. Further, it is frequently carried out to execute dynamic scanning by imaging CT inspection to provide dynamic information of circulation at a surrounding of a focus as visual information. By appearance of multislicing CT scanner in recent years, high speed scanning can be executed and therefore, it seems that dynamic scanning by imaging CT inspection will further frequently be executed in the future.
As one of the applied example of the dynamic scanning by imaging CT inspection, there is brain blood stream analysis (CT-perfusion) as shown by, for example, JP-A-2003-116843 or JP-A-2003-190148. The dynamic scanning is a method of providing a plurality of sheets of dynamic CT images by repeatedly taking an image of the same region of the head portion of a subject injected with a contrast medium. A time-intensity (CT value) curve (TIC: time intensity curve) representing a time sequential change of the CT values for respective designated regions is obtained by the plurality of sheets of dynamic CT images. According to the brain blood stream analysis, there are calculated parameters of a brain blood flow rate (CBF: Cerebral Blood Flow: a blood flow rate per unit volume and per unit time in the capillary of the brain tissue), a brain blood volume (CBV: Cerebral Blood Volume: a blood volume per unit volume in the brain tissue), a mean transit time (MTT: Mean Transit Time: a mean time period of passing blood through the capillary), a residue (Err: an index of err of shift of a measured value from an analyzing model) from the plurality of sheets of dynamic CT images. The calculated parameters are visualized as, for example, maps to subject to diagnosis.
Since the object portion of the brain blood flow analysis is the brain tissue, it is important not to output a result of measuring the principal blood vessel in the brain and not to reflect the CT value of the blood vessel to a result of measuring the brain tissue. The blood volume of the blood vessel is larger than perfusion of the brain tissue. Therefore, according to the brain blood stream analysis of the related art, generally, a pixel in the blood vessel region is removed by subjecting a result of analyzing the blood volume to a threshold processing (blood vessel removing processing).
However, in the case of the above-described method of removing the blood vessel of the related art, a partial volume of the blood vessel is widened by a filtering processing for removing noise executed in the midst of a processing of analyzing the tissue blood stream and a pixel bundling processing aiming at compression of image data, the pixel value of the blood vessel portion is removed thereafter and therefore, there poses a problem that an effect of the partial volume of the blood vessel remains at an edge portion of a contour contiguous to the removed blood vessel portion. The blood flow rate of the brain tissue is evaluated to be slightly larger by presence of the partial volume effect, which effects an influence on reliability of a result of measuring the blood flow rate.